Calculation of Correlation Functions in the Weak Coupling Approximation

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We have previously pointed out (1996, Phys. Rev. Lett.77, 798) that in the calculation of a correlation function C(t) by means of the fluctuation-dissipation theorem, much insight could be gained by writing the Fourier transform of C(t) as of the Fourier transform of the relaxation function multiplying the universal power spectrum of quantum noise at temperature T. Here, we show how this factorization leads to an immediate simplifying approach in the weak coupling limit near resonance. In particular, the time decay dependencies which appear are those associated with the Onsager classical regression theorem. Also, we throw further light on our previous assertion that there is never a quantum regression theorem. © 1999 Academic Press.

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Annals of Physics

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